In conventional film/screen radiography, an x-ray image is formed on film by exposing an object (such as a patient body part) to a source of x-rays. The developed film is then used by a physician for diagnostic purposes. In order to facilitate computer processing of an x-ray image on film, the film is digitally scanned to produce a digital x-ray image. The digital image can be processed, stored, transmitted to remote locations and displayed on a video monitor. One type of digital film scanner uses a laser to produce a laser beam which is scanned in a line across an information medium, such as radiographic film, as the medium is translated in a direction perpendicular to the line scan direction. Light transmitted or reflected from the film is collected and converted to an electrical image signal by a photodetector.
Laser film scanners are disclosed in U.S. Pat. No. 4,818,861 , issued Apr. 4, 1989, inventors Horiuche et al. and U.S. Pat. No. 4,568,984, issued Feb. 4, 1986, inventors Juergensen et al. The latter patent discloses the use of a cylindrical diffuse light collector located below a horizontally translated film which is scanned with a laser beam. The collector has a slot for receiving transmitted light into the collector cavity where the light is diffusely reflected to a photodetector by means of a fiber optic bundle. Such a collector is disadvantageous since dirt can enter the collector cavity through the light collecting slot and accumulate at the bottom of the collector cavity to cause streak artifacts. Moreover, the use of fiber optic bundles is expensive and disadvantageous to manufacture.
U.S. Pat. No. 2,821,103, issued Jan. 28, 1958, inventor G. C. F. Blet; U.S. Pat. No. 3,327,583, issued Jun. 27, 1967, inventors G. F. Vanderschmidt et al.; U.S. Pat. 3,648,056, issued Mar. 7, 1972, inventors T. B. Buttweiler et al.; U.S. Pat. No. 4,583,860, issued Apr. 22, 1986, inventor C. L. Butner; U.S. Pat. No. 4,868,383, issued Sep. 19, 1989, inventors A. F. Kurtz et al., disclose various configurations of light collecting and transmitting spheres and cylinders which do not solve these problems.
It is thus desirable that such streak artifacts be eliminated. It is also desirable that the light collector have high light collection efficiency, be easy and economical to manufacture and be configured so that photodetectors are shaded from scattered transmitted light.